This invention relates to synchronous motors, and particularly to synchronous motors having winding-energized stator poles with stator teeth projecting radially toward the magnetized teeth on a rotor carrying a permanent magnet.
Such motors and their operation are described in an article entitled "New Inductor Motor has Low Speed, Self-start and High Torque" by J. H. Staak, page 115 et seq. in the June 1947 issue of Electrical Manufacturing published by the Gage Publishing Company, New York, New York and in patents such as Reissue Nos. 25,445; 3,077,555 and 3,343,014. In all these patents and publications, the motors possess rotors with uniformly pitched teeth and stator poles with uniformly pitched teeth. In the Staak article and U.S. Pat. No. 3,343,014 the pitches of the rotor teeth and stator teeth are equal to each other. In U.S. Pat. No. 3,077,555 and Reissue No. 25,445, the pitches of the rotor teeth and the pitches of the stator teeth, although they are uniform, are not equal to each other.
Each of these types of motors has some disadvantages as compared to the other. For example, motors with unequally pitched rotor and stator teeth often exhibit lower torques and are not as easy to stop at predetermined angular positions. On the other hand, motors with equally pitched rotor and stator teeth are noisier and do not operate as smoothly as the other types. The equally pitched type motors exhibit higher spring mass resonances than the unequally pitched type motors. On the other hand the latter have far lower setting times.
An object of this invention is to overcome some of the disadvantages of one motor while retaining the advantages of the other. Another object of the invention is to improve synchronous motors.